1. Field of the Invention
The present invention relates to a light-emitting unit, in particular, of the type which includes a printed circuit board or substrate, a light-emitting element mounted on the board, and a lens to interact with light from the light-emitting element. The present invention also relates to an illuminator incorporating such a light-emitting unit as one of the constituent parts.
2. Description of the Related Art
The prior art in the field of electric illuminators teaches that an illuminator is obtained by mounting a light-emitting element on a printed circuit board, and providing a lens to interact with the light emitted from the light-emitting element. With such illuminators, various kinds of techniques have been developed in order to improve the lighting efficiency so that the selected area is irradiated brightly, or to avoid uneven irradiation by adjusting the configuration of the lens. As one possible way to achieve the improvement of the lighting efficiency, the light-emitting element may be surrounded by a highly reflective metal member so that the maximum amount of light from the element is directed toward a convex lens (in this connection, refer to Japanese patent application laid-open No. H04-28269, for example).
For adjustment of the lens configuration, a resin in a liquid state for making the lens is caused to drop into a recess provided on the board supporting the light-emitting element, and then the resin is hardened. In this manner, the height of the lens, for example, can be standardized (in this connection, refer to Japanese patent application laid-open No. H07-231120, for example).
As noted above, the performance of conventional illuminators has been improving. In addition, when a light-emitting diode is employed as the light source, the illuminator consumes a smaller amount of energy and lasts a considerably longer life (the life can be substantially semipermanent). However, the applicable fields of the conventional illuminators are unduly limited because of their distinct directivity. As an example, supposing that two light-emitting elements are mounted on the board, with one on the obverse side and the other on the reverse side, the illuminator only produces two light beams which may typically travel in the opposite directions. With such an arrangement, it is impossible to realize uniform irradiation in all the directions around the light source.